Aircraft landing gear



Aug. 9, 1949. RF. PAXHIA ET AL AIRCRAFT LANDING GEAR Filed June 24, 1946 IN V EN TORS M H M Y wu E NR N A0 R ME EG m w A Patented Aug. 9, 1949 nrn'cmm'r LANDING. GEAR Emanuel .F. Paxhim. Kenmore, and George..M. ..Cash, .Hairmburg,.Ni 3L, assignors to Curtissw righ'tCprpora't-ion, a corporation"of-Delaware Appliea'tiuirfluniZ'i, 1946, Serial No. 678,971

I 'l il 'Claims.

.Thisinventiomrelates tolaircraf-t landing-gear andmorepartimflarly-to acentering=device .ior a swivel.- gear, suchrfor example-as. :the: gear tor the nose wheel of an aircraft provided :with a tricycle landing gear. 7

Asxthe weight and 'iandingtspeeds ofcaircraft have-increased; ithas become necessary to center or. to align casteringmheelswith thenormal landingpathcoffltheeaircraft.i This isnecessary in order to avoideimposition;ofiexcessive loads and to s prevent. starting .of violent: oscillation .or shimmy-.ofthe wheel whichmayoccurif a castering wheel is allowed to contact the ground while misaligned- Suchoscillation not only-.-imposes .excessiveloads on thestructure .but in some-cases may resultin loss .of..control of the aircraft. Centering of such a wheel is also neoessaryimcases of retractablexgearin. order that the wheel may properly-.ienter the .PQCkEtuiIltO which. ibis retracted. In order totacilitate.steeringthe aircraft on the ground it isdesirablethatthe wheel beallowed .to .caster free. .oLany. centering .action.

. The present inventioniprovideslanimproved centering arrangement by. which .the. weight 'of the wheel. or :othenmeansare'; .enective. .to. center the wheel when the'aircraft is in flight, and in which the centering means are automatically released vas'the wheel makes contact (with the ground. Centering". is accomplished by a pair of complementary cams which arebrought together, by linkage connectedbetweenfixedanduXtensible parts of the 'landinggear compressionstrut; when the latter-"are intheirrelativelyextended-relation occurring in flight," andwhich are-separated to allow free-castering (if the wheel assoomas t-he 2 strut iscompressed on 'landing.

The arrangement provideafor 'a-relatively short stroke ofthe 'movab1e=one' of the cams-vascom- 'pared" withthe operating stroke of the compression strut, with the res'ultthatthe structure may -'be' compactand of light weight. The foregoing and other objects and advantages-"ofthe invent-ion will become apparent trorn the following-description'of the typical embodiment showni-n the accompanying drawings, wherein:

Fig. 1 isa-fragmentaryside elevationof a landing gear with certain partsappearing in section 'Fig. 2 is afragmentary substantially-plan view in the plane indicated -at-2+2 in' Fig. 1;

Fig; 3" a-vertica'l sectional view taken along line of Fig. 2::and,

Figs. 4 "and 5 are cross se'ctional viewstaken along lines 4 -4 and-5-'5; respectivelyfof Eig. 3. As shownainthedrawingsthe supportingassenn bly-"of' the gear-comprises a telescoping shock 2 strut [0 having a cylinder] Land a piston .12 connected by ascissorsi linkage v[3.1011lziolding'the telescoping parts against. relative angular mo ment; To the lower end'of member 12- issecufed a housing (4 supportingbearing'si l5 andilliior journals I1 and H! of a castering swiveledrorl; IS in which the landin wheelZ l, or otherlanding element is mounted. As shown Tin L'Eig'." 3i'the journal I8 is provided with a shoulder.j22;for thrust engagement upon the bearing"l6. 7

Between bearings l5 and-'16 and extending around intermediate portion 2350f the"shank'-of the fork are a pair oficam sleeves 24"and 25:11aspectively provided with diametrically ;oppos'ed cam lobes ,26 and complementarycamrecesss fl, Cam sleeve '25 issecured' by suitable-meansgsucl'i as'keys 28, to shank part 23'of'the forkywh-ile cam -sleeve"-24 is slidable and rotatable on pant-'-23. It is also slidable within the bore-'ofhousing-H, but is-held against rotation-relative thereto "by having splines 29 extending into 'grooves at in the housing side walls. *Trunnion'sr32 carriedby the cam -s1eev'e24 extendthroughslotsfil formed in the grooved portion of the 'housing 'side wail, and are connected by pivoted links 33 tc? :lever arms 3d and-=35. Thelatterarevfixedvto azatransverse rock shaft 36 journalled' ioh th'et housing-1.4.. .In order to seal theuslots 31-:against.aingnessslof foreign matter, closure shieldsfiilflrare provided, being. carried'by thetrunnions;32.

A1tube 3.9 afiixed 'tothe rshoclc.stmt-.acylinderz-j1 housesthe upper end of a rodEA-I iwhich iSfDiV-tfid at 42-to lever;arm- 34. tThehoused endofitheirod hasadjustably threadedrthereto a nutzor other stop member 43 for engagement with ashoulder 44 at the bottom of tube 39 when theashockstrut piston I2.approaches.=fullyrextended relation! to cylinder 1 l..x;I-n moreretraeted positions of piston l 2 the: stop :43 is spaced. afrom' -theshoulder -as shown in Fig. .1 For holding itheqcamzsleevefn spacedbeneath cam sleeve- 25, withcam surtaces '2 6,, =21. fully disengaged, resilient meanscinnthe 1f orm-of: tension springs -45 are connected-between t'he: housingttandieach of arms. 34y,3,5.

.-:In operation it 'wi1l.-b.e understoodthatcwhen .nozcompressive :load is appliedqto theshockistrut =1l'0, as whenxtheaircraftisin flight; the members 1 l, !:2:.wi11 b.e;in:extendedrelation: andrthat when such acicompressive load is appliedas whenrthe :aircraft iszsupported on the ground the landing gear thetmember'si'l l l2 inormal'ly-zwillebefimithe partially retracted: relation :shownsin Fig. lsrthe :degree of retraction varying with ztheramonnteof Plead-tozenable .thesstrut'sto absorbzshncksrincidnt torlandingron travel we the: 'aircrafteovernmeven ground. It will also be understood that, if desired, when in flight the entire landing gear assembly may be moved to a retracted position within the aircraft by suitable retraction means, not shown.

As the aircraft takes off and the shock strut approaches full extension, the stop 43 engages shoulder 44, so that during the terminal phases of the extension the lever arms 34, 35 are moved counterclockwise, bringing cam sleeves 24, 25 into engagement. During this action the cam lobes 24 will ride upon the surfaces of cam recesses 21, finally nesting therein, rotating the wheel carrying member l9 so that the wheel 2| is centered, that is, aligned with the longitudinal axis of the aircraft, and holding the fork-wheel assembly thus centered.

However, as soon as the shock strut is compressed or retracted the cam sleeve 24 will move to the disengaged position shown in the drawings, by action of both gravity and resilient means 45. Accordingly as soon as the aircrafts ground weight is upon the landing gear the fork is free to rotate in bearings l5, l6, so that there is no interference with steering of the aircraft on the ground.

It will be noted that by reason of the play connection afforded between the rod 6| and strut member II by stop elements 43, 44, and also by reason of the lever advantage provided by arm 34, the travel of the cam sleeve 24 is short relative tothe normal telescoping movement of the strut element l2 between extended and retracted positions. Accordingly the cam surfaces 25, 27 may be small and the entire assembly may be encased in a housing M of small dimensions and light weight. Adjustment of the wheel centering mechanism, to render it operative and inoperative at the desired points of strut extension and retraction may be accomplished by adjusting the stop nut 43 axially along rod 4|.

The arrangement may be applied either to a free castering swivel landing gear or to a gear whose swivel action is controlled by suitable snubbing, steering or other control means. For example an arm 46 secured to the shank of fork It may be extended to such control means if desired. It will be understood that the structure and arrangement herein specifically shown and described are merely illustrative of the inventive principles involved, and that these principles may be otherwise embodied without departing from the spirit of the invention or the scope of the appended claims.

We claim: 1. In an aircraft landing gear, a compression strut comprising telescoping members, one of which is connected to the aircraft and another of which is retractable relative to the first mentioned member under ground load, a landing wheel carrying member having a shank swiveled to said other telescoping member, a centering cam sleeve afiixed to said shank, a cooperating cam sleeve axially and angularly movable relative to said shank and keyed against rotation relative to said other telescoping member, a lever pivoted to the latter member and a pivoted link connecting the lever with said cooperating cam sleeve for moving the latter into and from engagement with said centering cam sleeve, a play connection between the lever and the telescoping member connected to the aircraft for effecting engagement of said cam sleeves upon extension of the strut, and resilient means between the lever and the other telescoping member for disengaging said cam sleeves upon retraction of the strut.

2. In an aircraft landing gear, a compression strut comprising telescoping members, one of which is connected to the aircraft and another of which is retractable relative to the first mentioned member under ground load, a landing wheel carrying member having a shank swiveled to said other telescoping member, a centering cam sleeve affixed to said shank, a cooperating cam sleeve axially and angularly movable relative to said shank and keyed against rotation relative to said other telescoping member, a lever pivoted to the latter member and a pivoted link connecting the lever with said cooperating cam sleeve for moving the latter into and from engagement with said centering cam sleeve, an adjustable play connection between the lever and the telescoping member connected to the aircraft for effecting engagement of said cam sleeves upon extension of the strut, and resilient mean between the lever and the other telescoping member for disengaging said cam sleeves upon retraction of the strut.

3. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing Wheel carrying member swiveled to the second member, wheel centering means comprising a first cam fixed to the wheel carrying member and a second cam engageable with the first cam, a lever pivotally connected to said second member and the second cam for moving the latter to and from a position of wheel centering engagement with the first cam, a play connection between the first member and the lever for effecting disengagementof the cam upon retraction of the supporting assembly, and resilient means for efiecting engagement of the cams upon extension of the supporting assembly.

4. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a econd member retractable relative thereto under ground load, a landing wheel carrying member swiveled to the second member, wheel centering means comprising a first cam fixed to the wheel carrying member and a second cam engageable with the first cam, a lever pivotally connected to said second member and the second cam for moving the latter to and from a position of wheel centering engagement with the first cam, an adjustable play connection between the first member and the lever for effecting disengagement of the cams upon retraction of the supporting assembly, and resilient means for effecting engagement of the cams upon extension of the supporting assembly.

5. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing element carrying member swiveled to the second member, centering means comprising a first cam fixed to said carrying member and a second cam engageable with the first cam, a lever pivotally connected to said second member and to the second cam for moving the latter relative to the second member to and from positions of centering engagement with the first cam, and a connection between the lever and said first member for effecting disengagement of said cams upon retraction of the supporting assembly.

6. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing element carrying member swiveled to the second member, centerin means comprising a first cam fixed to said carrying member and a second cam engageable with the first cam, and a play connection between the first member and the second cam for moving the latter relative to the second member from engagement with the first cam upon retraction of the supporting assembly.

7. In an aircraft landin gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing element carrying member swiveled to the second member, centering means comprising a first cam fixed to said carrying member and a second cam engageable with the first cam, and an adjustable play connection between the first member and the second cam for movin the latter relative to the second member from engagement with the first cam upon retraction of the supportin assembly.

8. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing element carrying member swiveled to the second member, centering means comprising a first cam fixed to said carrying member and a second cam engageable with the first cam, a play connection between the first member and the second cam for moving the latter relative to the second member from engagement with the first cam upon retraction of the supporting assembly, and means to effect engagement of the cams upon extension of the supporting assembly.

9. In an aircraft landing gear having a member displaceable under ground load, a landing element carrying member connected by swivel means to the aircraft, centering means comprising relatively movable and engageable cam elements associated with the swivel means, a lever for effecting relative movement of the cam elements into and from centering relationship, and means for moving the lever in response to movement of said displaceable member under decreasing and. increasing ground loads respectively.

10. In an aircraft landing gear having a member displaceable under ground load, a landing element carrying member connected by swivel means to the aircraft, centerin means comprising relatively movable and engageable cam elements associated with the swivel means, a lever for effecting relative movement of the cam elements into or from centering relationship, and means including a play connection for moving the lever in response to movement of the displaceable member in approaching and departing from the unloaded position thereof, the play connection freeing the centering means from the displaceable member during other phases of the latters motion.

11. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing Wheel mounting member swiveled to the second member, wheel centering means comprisin a cam part and a cam follower part one of which is carried by the wheel mounting member and the other of which is carried by the second member, and an operatin lever for moving one of said parts relative to the second member into and from centering engagement with the other of said parts, said lever being pivoted to the second member and operated by'the relative movement of the first and second members to disengage said parts from centering relationship when the supporting assembly is under ground load.

12. In an aircraft landing gear, a supporting assembly comprising a first member connected to the aircraft and a second member retractable relative thereto under ground load, a landing wheel mounting member swiveled to the second member, wheel centering means comprising a cam part and a follower part one of which is carried by the wheel mounting member and the other of which is carried by the second member, and a play connection between the first member and one of said parts for moving it into and from centering en agement with the other of said parts, said play connection elfecting the movement into and from centering engagement respectively only during the terminal phase of extension and the initial phase of retraction of the second member, and said play connection providing for movement of the second member free of the centering means during other phases of extension and retraction.

13. In an aircraft landing gear, a member connected to the aircraft body, a member carrying a landing wheel, and an intermediate member connected to the aforementioned members for transmitting ground loads between the landing wheel and the aircraft body, said intermediate member having a shock absorbing connection with one member of said aforementioned members providing for substantially vertical relative movement, said intermediate member havin a. swivel connection with the other member of said aforementioned members providing for turning of the landing wheel about a substantially upright axis, a pair of cam elements adapted to be engaged for centering the landing wheel about the swivel axis, said cam elements being nonrotatably mounted respectively on the intermediate member and said other member, means connecting said one member with one cam element for engaging it with the other cam element to effect said centering of the landing wheel upon movement of said one member to its limit position relative to the intermediate member in the direction resulting from removal of ground load from the landing gear, said connecting means including a play connection providing for movement of said one member relative to the intermediate member free from said one cam element when the landing gear is under ground load.

EMANUEL F. PAXHIA. GEORGE M. CASH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,379,173 Miller June 26, 1945 2,394,496 Stephan Feb. 5, 1946 FOREIGN PATENTS Number Country Date 465,714 Great Britain May 13, 1937 

